MySql如果然后在Select语句中

Question

我想在mysql select中使用IF THEN语句,但无法弄明白.当还没有评论时,评论创建的值应该是项目本身的创建值.这是查询:

SELECT item.*, 
  count(comments.itemid) AS commentcount, 
  max(comments.created) AS commentcreated 
FROM table_items AS item 
LEFT JOIN table_comments AS comments ON (comments.itemid = item.id) 
WHERE item.published=1 
GROUP BY item.id 
ORDER BY item.created DESC

我想到了这个,但它不起作用:

...
, IF max(comments.created)!='NULL'
THEN max(comments.created) AS commentcreated
ELSE item.created AS commentcreated
END IF;
FROM .......

做这个的最好方式是什么？

Answer 1

可以使用 IFNULL

IFNULL(max(comments.created), item.created) AS commentcreated

要么 IF

IF(max(comments.created)='NULL', max(comments.created), item.created) 
AS commentcreated